The assessment comes as ousted Ukrainian President Viktor Yanukovych gave a defiant speech on Friday from Russia, insisting he is still the country's legitimate elected leader.

Also, in Ukraine's Russian-majority southern Crimean region, the possible threat of secession escalated tensions as the government accused Russian Black Sea forces of trying to seize two airports.

And Russian lawmakers introduced bills Friday that would make it simpler to annex new territories into the Russian Federation.

"The idea of respecting territorial integrity is an international norm that President (Vladimir) Putin and Foreign Miniser (Sergey) Lavrov have often talked about, usually in criticism of the United States and Western countries," McFaul said.

"Obviously in previous times -- and Georgia comes to mind in 2008 -- when they deem it to be in their national interest, they will violate that norm."

In a brief conflict over the breakaway South Ossetia province, Russian forces decisively overran Georgian forces in about a week's time. Many of the separatists in that region had Russian ties.

The same could hold true in Crimea where ethnic Russians outnumber ethnic Ukrainians, McFaul said.

"It's a revolutionary situation that needs to be handled very delicately," he said. "Nothing could be worse than all-and-all combat between" the two groups.

McFaul said Western nations need to de-escalate the tensions in Crimea, but also understand that Putin is pragmatic.

"He's not a risk-taker. I think therefore we need to leverage that and make sure he understands the consequences of a genuine all-out Russian military invasion of Ukraine," McFaul said without explaining what they would be. "That's ... a scenario that neither the West or Russia desires."